online search queries as a proxy for contagion

2020-04-27

In the current coronavirus outbreak, governments face hard decisions on how to best combat the spread of the virus. This note proposes a way to capture the spread of contagion, so as to quickly evaluate policy impact.

Policymakers are operating under considerable uncertainty when trying to weigh costs and benefits of policy choices. Attempts at causal estimation of the effects of different interventions have been few and far between. Randomized trials have been, more or less, out of the question due to the need of acting fast and most of the other classic techniques used to estimate causal effects, are not applicable due to the lack of reliable data.

Swedish economists Dany Kessel, Adam Altmejd, Elisabet Olme, Elin Molin, and Nils Lager show examples of how online search queries can be used as a proxy for contagion to quickly evaluate policy impact. Since Covid-19 has many similarities to the flu, but the flu has a shorter incubation period, queries for flu symptoms respond quicker. A simple comparison between Sweden and Norway shows that search intensity decreased faster in Norway following the stricter lockdown imposed there.